1. Field of the Invention
The present invention relates to a hollow-cast component which encloses at least one hollow space.
2. Brief Description of the Related Art
When manufacturing high precision cast components, it is necessary that any existing cores are supported in the case mold in as stable a manner as possible. With rising requirements on manufacturing accuracy, the necessary dimensions of the core supports therefore in general rise also.
Because of the core supports, openings are created in the component's walls during casting. In many cases, these openings are not necessary for the component's function, or at least are not necessary to the degree that they are provided. To the contrary, excessively large and numerous core openings like these are, in most cases, undesirable since, on the one hand, they weaken the mechanical stability of the components, but, in particular, also represent undesirable leakage points.
As an example, reference is made in this context to a cooled gas turbine blade whose interior has been provided with complex cooling air channels. To create the internal structures of such blades, cores must be fixed very precisely and in a very stable manner in the cast mold. It is therefore desirable to secure the core, i.e., on the side of the blade base and on the side of the blade head, with large core supports. The large core openings thus created also facilitates the removal of the core from the hollow-cast blade and permit easy inspection of the hollow space.
But the cast component created in this manner has openings that are undesirable for its proper function. Although in the above mentioned example of a cooled gas turbine blade, relatively large openings at the blade base are desired to bring cooling air into and remove air from the blade interior, openings that are desirable or even necessary in terms of production technology, especially on the blade head, often lead to damaging cooling air leakage.
In the past, the goal was to keep the core supports as small as possible at those places where an opening was not to be provided in any case. But this solution increases casting tolerances. Very small bores are not processed any further, while a closure piece is welded or soldered over the hole in larger openings. The latter approach is not without problems, especially if the component is used in the hot gas part of gas turbines, i.e., the closure piece and the seam are directly exposed to the hot gas. High temperature alloys, as those used for gas turbine blades, often are hard to weld also. There is therefore a latent danger that the attached closure piece separates from the component, and the previously closed opening is again open. This risk of a separating closure piece is especially high if it is attached to the head of a rotor blade, for which an additional centrifugal force is in effect. The closure piece also can be separated if a rotor blade brushes against the housing, or if a guide blade brushes against the rotor elements.
Especially in the above described example of a gas turbine blade, this failure of the closure piece may result in a sensitive shift in the cooling air balance, potentially resulting in a component failure with serious consequences as a result of overheating.
On the other hand, as was described above, the core openings cannot be completely eliminated without having to accept drastically greater casting tolerances and drastic reduction in the designer's freedom when designing the hollow spaces, i.e., when designing the component cooling.
It would therefore be desirable to use the largest possible core supports because of production technology considerations, while on the other hand the resulting core openings must be reliably closed. The current state of the art does not provide any suitable possibility for accomplishing this.